Use of mobile radio communication systems is pervasive in modern society. The network infrastructures of cellular communication systems, for instance, have been deployed over significant portions of the populated areas of the world, readily accessible through which to communicate. Cellular communication systems generally make efficient use of bandwidth allocated thereto for communications as relatively low power signals are generated to effectuate communications between mobile stations and the network infrastructure of such systems. The network infrastructure of a cellular communication system includes a plurality of spaced-apart base stations, each defining a cell. By transmitting only low-power signals, the same channels are reusable within relatively short distances. And, channels are reused according to a so-called, cell re-use scheme.
As a mobile station moves, or is otherwise repositioned, within an area encompassed by a cellular communication system, there is sometimes a need to hand-off communications between different base transceiver stations or other radio sub-systems entities to permit continued communication of a mobile station. In a hand-off of communications between cells, i.e., the radio sub-systems that define such cells, a decision must be made both as to which radio sub-system to hand off communications and when to hand-off the communications.
A GSM (Global System for Mobile communications) is an exemplary cellular communication system. A GSM system operates in general conformity with a GSM operating specification that sets forth, amongst other things, operating protocols and requirements required of devices operable in such a system. GSM technologies were originally, based upon circuit-switched technologies and provided circuit-switched connections between communication endpoints. However, GPRS (General Packet Radio System) and, more recently, EDGE (Enhanced Data for GSM Evolution) capabilities have been added to provide high-speed, variable-rate data communication services that make use of packet-switched technologies. EDGE is, in essence, a superset of GPRS and provides the capability of packet-based user data interchange by way of the network infrastructure of a GSM network and a radio air interface defined therein. EDGE and GPRS data communications regularly exhibit characteristics that differ with the characteristics of voice communications, conventionally communicated by way of a GSM network using circuit-switched connections and technologies. One significant characteristic, in general, of data communications is their bursty nature. That is to say, data is typically communicated in bursts. And, in a system that utilizes time slots, such as GSM, multiple, contiguous time slots are sometimes needed to communicate the data in a burst.
In existing GSM operation, hand-off is generally determined based upon determination of RSSI (Received Signal Strength Indication) levels of signals communicated by a base transceiver station or other radio sub-system element of the network infrastructure of the GSM system. Determining to where, and when, to hand-off communications based upon RSSI levels works well when voice information is communicated in a GSM system. Agile handover mechanisms are presently available to move voice communications using circuit-switched technologies amongst radio channels when signal quality degrades, or bit error probability increases, beyond selected thresholds. However, such existing hand-off mechanisms are sub-optimal when selecting hand-off of data communications. That is to say, corresponding, agile hand-off mechanisms are not part of the GPRS/EDGE specifications. Data communications, as just-mentioned, regularly require multiple, contiguous time slot allocations for their effectuation, not single time slot allocations, more typically allocated in voice communications.
A manner better to optimize radio sub-system selection for data communications, taking into account the characteristics regularly exhibited by, or required of, data that is to be communicated would therefore be advantageous.
It is in light of this background information related to radio sub-system selection in a radio communication system that the significant improvements of the present invention have evolved.